My invention relates to improvements in keys and key barrels for conventional lock cylinders and cylinders which have key-removable cores. Such well known mechanisms use pin tumblers which are evenly spaced in a single row along the length of the key barrel. In particular, my invention relates to keys having new cross-sectional profiles and the corresponding key barrels suitable for such keys.
In general, my invention relates to conventional key cylinders and cylinders which use key-removable cores of the type described in U.S. Pat. No. 2,814,941 (Best), U.S. Pat. No. 3,603,123 (Best), and in G.L. Finch's Service Manual entitled "Servicing Interchangeable Cores," revised in 1988.
The above-noted key-removable, interchangeable cores have been in widespread use in the United States for more than 20 years. Such interchangeable cores permit unskilled persons to rekey locks (i.e., block-out existing keys) in 10 to 15 seconds without opening the door or removing the cylinder body. To achieve the convenience of interchangeable cores, all interchangeable cores in a given system are pinned for release from their housings by a single "control key." The control key is actually a "top" master key whose sole function is limited (15 degree rotation) to operation of the blocking lug which retains the core in the cylinder body. Control keys are not visually distinguishable from other keys in the system. Typically, the core is also pinned to one or more master keys and to a tenant key. Such a system usually requires three or four pin segments in each pin column, an arrangement which offers very limited pick-resistance.
In large institutions such as colleges, hospitals, etc., door lock security is threatened by the circulation of unauthorized keys. In relative terms, lock-picking is a minor consideration. While a building manager's ability to instantly rekey with interchangeable cores clearly promises a degree of key control, a serious problem exists in universities, for instance, where students can have unauthorized copies of their keys made at a hardware store or lockshop. The most practical protection against this security compromise resides in proprietary keys (patented) which only can be made and duplicated by the lock maker or an authorized locksmith, (a) because key blank distribution is restricted by the manufacturer, (b) because the key blank cannot be bitted (finished) on machines in current use by keymakers and locksmiths. An additional level of protection exists if prior art key blanks cannot easily be modified or counterfeited to enter proprietary key slots and, when proprietary key blanks cannot be bitted in a single operation on a single machine. Further, although not generally known, master keying technology, similar to that employed in generic interchangeable cores, may reduce the number of usable change keys in a single system to between 2 and 5% of those available in non-master keyed cylinders. Such a limited number of key changes may not be enough to guarantee trustworthy locks in a medium-sized institution. Accordingly, when too few key changes are available, there is no certainty that a key to one lock will not inadvertently operate other locks on the premises.
Key removable, interchangeable cores are manufactured by most American lockmakers. Core interchangeability is usually limited to the housings of a single manufacturer (i.e., SARGENT cores in SARGENT housings, YALE cores in YALE housings, etc.). However, the interchangeable cores referenced in the above-noted Finch's Service Manual are generic in the sense that a BEST core fits (i.e., interchanges with) the housings of ARROW, FALCON, EAGLE and others. Likewise, the cores of ARROW, FALCON, EAGLE and others fit the BEST housings, etc. without onsite modification.
Further exacerbating key control problems is the fact that the above-mentioned generic cores all use common, warded key slots which are suited to flat keys which are grooved on both sides. 100,000 groove patterns are in the public domain. Some milling differs are so minute when compared with each other, that they cannot perform their security function as intended, particularly when the key slots are worn or were not broached to close tolerances.
Typical keys for generic cores are milled on two flat surfaces. The key slot warding reflects the milling pattern of the lowest level keys (i.e., the keys assigned to tenants). Master keys are thinner sections which are side milled to enter (pass) selected groups of key slots. The top master key and the control key must enter all key slots in a given system, which may number in the thousands.
Typical hierarchical order of keys/sections:
CONTROL KEY will change all cores in a system.
GRAND MASTER KEY will unlock any lock in the system.
MASTER & SUBMASTER KEYS unlock only specific groups of locks.
TENANT KEYS unlock one lock only. In large systems tenant keys are bitted on several related (family) key sections under each master key.
Control and Grandmaster Keys may be bitted on the same key blank section. Master key blank sections (because they must pass two or more key slots that differ) are usually thinner sections.
However, in practice, problems arise in such systems since blank manufacturers do not restrict the distribution of key blanks used to bit or cut the keys for the generic cores. Further, hardware stores and some keymakers only stock master key blank sections, which of course will enter all cores in a group. Some will enter all cores in the system. Some will enter cores in every generic core system.
Thus, there are tens of millions of generic interchangeable cores on doors throughout America. Statistically, even the lowest level keys (i.e., tenant keys) can be expected to unintentionally operate thousands of interchangeable cores in systems other than their own.
In addition, since bitting combinations for master keys are randomly selected, a tenant key from almost any generic core system, when copied on a control key blank section, has the potential of operating cores, or removing cores from their housings in other systems across the street or across the country.
U.S. Pat. No. 2,049,548 (Swanson) discloses a guard tumbler which is comprised of two members which are biased toward the key slot by a compression spring. The guard is similar in construction to that of conventional pin tumblers except that it is longer than the other tumblers and its operating chamber extends to the bottom of the key slot, as shown in FIG. 1. In order to effect release of the key barrel, a key having a notched lip and a supporting wing is employed. The lip is provided with the usual notches (bittings) for positioning the tumblers and a guard releasing notch is formed in the inner end of the lip, between the lip and the key bow. Because of the employment of a guard releasing notch, the supporting wing is included to obtain sufficient strength in the key. FIGS. 10 and 11 of Swanson show variations on the form of the angularly shaped key slot for receiving a like shaped key blade. Thus, the portion of the key blade which corresponds to the lower portion of the key slot in FIG. 10 and which corresponds to the horizontal portion of the key slot in FIG. 11 serve the same purpose as the supporting wing of the first embodiment.
However, FIGS. 10 and 11 both show angular keys (dotted lines and see claim 7) which are notched forward of the bow for the guard tumbler. This leaves only 4 tumbler positions on the key which can be bitted differently. 10 bitting increments to the 4th power can yield a maximum of 10,000 theoretical key changes; not near enough for contemporary requirements.
The key in FIG. 10 has parallel legs of the same width. This permits key duplication on conventional bitting machines. The skewed key slot, however, precludes placing secondary wards or tumblers directly beneath the horizontal leg of the key in line with the primary tumblers.
The key in FIG. 11 has right angle legs of the same width. The key cannot lay flat, an important consideration for consumer acceptance in the 1990's.
U.S. Pat. No. 4,683,740 (Errani) is similar to Swanson. In particular, upon inserting a picking tool (see FIG. 3) in an attempt to bring the pins to shear at the key barrel periphery, one or more pins are unavoidably extended into the cylinder body, thus inhibiting key barrel rotation.
However, the Errani key's horizontal portion separating a bitting portion from a support portion is uniquely undercut to compliment a restricted-access key slot. The secondary key differing elements are bitted on both sides of the support portion. All blade portions relative to the key bow are on a single plane. The restricted access key slot requires a key with a much wider support portion than usual which greatly limits the number of key changes that can be generated by the remaining relatively shallow bitting portion which positions the primary tumblers. Errani's horizontal portion cannot be bitted on its underside.
U.S. Pat. No. 4,416,128 (Steinbrink) relates to an arcuate skeleton in a flat key to resist the effectiveness of a pick-gun.
U.S. Pat. No. 2,814,941 (Best), U.S. Pat. No. 3,603,123 (Best) and U.S. Pat. No. 4,294,093 (Best) each relate to key-removable lock cores employing the standard key slot.